Process for the production of lightweight polyurethane moldings

ABSTRACT

A low density RRIM/RIM article formed of rigid foamed polyurethane which has incorporated in it, hollow glass microspheres with a compressive strength greater than 4,000 psi and a maximum size of 120 microns. This low density RRIM/RIM fascia may have physical properties and continuous high gloss painted outer skin comparable to conventional RRIM/RIM products while having reduced density in comparison to such product.

FIELD OF THE INVENTION

This invention relates to methods of RIM molding processes and resultantmoldings having high impact strength and capable of quality surfacefinishing for fascias of automobiles.

BACKGROUND OF THE INVENTION

Reaction Injection Molding (RIM) is a process involving filling a closedmold with highly reactive liquid starting components within a very shorttime to produce a rigid microcellular product having a continuous outerskin. The RIM process is important in the production of externalautomotive body components.

The RIM process involves the mixing of a polyisocyanate component with aisocyanate-reactive components and simultaneous injection of thismixture into a mold for subsequent rapid curing. The polyisocyanatecomponent is typically based on a liquid polyisocyanate. Theisocyanate-reactive component contains a high molecular weightisocyanate-reactive component, typically a polyol and/or an aminepolyether and usually contains a chain extender containing amino and/orhydroxyl groups.

The properties of the resulting product are dependent on a large numberof variables such as the nature of the starting liquid components, theamount and quality of nitrogen dissolved in the isocyanate-reactivecomponent (nucleation) and the amount and character of other additiveswhich may include a variety of fillers. Such fillers may includematerials such as fibreglass, mineral fillers or solid and/or hollowmicrospheres of a glass or ceramic material.

The RIM process is a complex process. It is sensitive to reactionconditions such as the presence and type of nucleating agents, theliquid reactants etc. Moreover, the product produced, especially forexterior automotive applications, have stringent requirements.Automotive fascias must have mechanical properties in order to pass therequired strength, thermal, impact, durability tests etc. Exteriorautomotive components must also have a highly decorative finish providedby high gloss painting. For example, a fascia for an automobile musthave a continuous high gloss outer skin, be lightweight and pass impacttests as required in various jurisdictions.

Fascias and other automotive products can be provided by other lessexpensive molding processes such as from thermoplastic olefin materials.Generally the advantages of such materials is in price and densityreduction rather than quality. An advantage of RRIM/RIM moldings haveover thermoplastic materials is the ability to sand the surface of themolded product to remove all visible parting lines without producingsurface defects. The problems encountered with other low density fillersproducing low density RRIM/RIM products for automotive exteriors was thepresence of pitting on the surface of the painted part at the sandedareas. This pitting is due to the breakage of the low density fillers.Therefore, there is a considerable advantage to produce a RRIM/RIMautomotive fascia which maintains the surface and physical qualities ofRIM products but which has a density and price comparable withthermoplastic olefin materials.

Due to the weight and cost advantages of thermoplastic olefin materialsfor fascia products, there has been considerable previous work done inthe efforts of decreasing both cost and density of polyurethaneproducts.

For example U.S. Pat. No. 5,244,613 issued Sep. 14, 1993 to Hurley etal. discloses the use of expanded organic microspheres encapsulating ablowing agent as means of reducing the density of a rigid RRIM molding.U.S. Pat. No. 3,866,653 issued 1975 to Ahmad discloses the use of hollowglass or ceramic microspheres in an elastomeric polyurethane to be usedin the cavity of a pneumatic tire. U.S. Pat. No. 4,839,393 issued Jun.13, 1989 to Buchanan et al. This patent discloses the use of glass beadsand/or bubbles to be mixed with polyurethane foam chips as a filler toincrease the volumes of foams while controlling the lightness in weight.These polyurethane foams are not of the rigid type as utilized forautomotive exterior components. U.S. Pat. No. 4,539,345 issued Sep.3,1985 to Hansen discloses the use of glass bubbles as a filler formoisture curable polyurethane compositions to be used as adhesives,coatings, sealants or casting resins.

More recent research into the production of a rigid RIM product hasresulted in a modified chemical system to produce polymers of greaterstrength and incorporating, as dual fillers, hollow ceramic microspheresknown to cause pitting and wollastokup, a reinforcing filler with poorimpact properties.

SUMMARY OF THE INVENTION

The present inventors have found that utilizing a specially selectedfiller within conventional polyurethane reaction procedures producedproducts with lower density while maintaining the same physicalproperties. The painted appearance of these products meet or exceedmeasurable appearance criteria or rigid RIM fascias molded withconventional fillers and/or other types of hollow glass and/or ceramicmicrospheres. The selected filler was a hollow glass microsphere havinga maximum size of 120 microns and a compressive strength of more than4,000 psi.

Thus, according to the invention we provide a method of preparing arigid article of foamed polyurethane, for example, of a polyurethanehaving an unfilled flexural strength of 30 kpsi or more, having acontinuous outer surface skin, the method comprising mixing an organicpolyisocyanate-reactive component to form a mixture in a closed mold,allowing the components to react and removing the product from the mold.The improvement involves using up to 6% weight, and preferably from0.5-4.% by weight (most preferably 1.5-3% by weight) based upon themolded product of a hollow glass microsphere with a compressive strengthof less than 4,000 psi and maximum size of 120 microns. Preferably theisocyanate reactive component comprises an isocyanate-reactive componentcomprising at least one compound containing at least two isocyanatereactive groups, dissolved nitrogen in an amount sufficient to produce amolded product having a density of at least 0.80 g/cc.

The mixture may also contain up to 30% weight, (preferably 4-20% byweight) based upon the weight of the molded product of a reinforcingfiller to enhance physical and thermal properties. It has been foundthat the use of the above microspheres; (i) may significantly enhanceand increase the quantity/quality of dissolved nitrogen in theisocyanate-reactive component, (ii) may enable uniform density withinthe part, (iii) may enable the painted product to have a continuousouter skin without pitting, and (iv) may allow for significant reductionin density of the moulded polyurethane part.

A suitable polyisocyanate is an aromatic isocyanate prepolymer.Particularly preferred is the liquid 4, 4'-diphenylmethane diisocyanate(MDI), diphenylmethane diisocyanate (MDI) (2,2; 2,4) and polyurethaneprepolymer.

The substance reactive with the said polyisocyanate is a polyetherpolyol system containing minimally an aliphatic amine and an aromaticdiamine. This system is a blend of hydroxyl terminated poly(oxyalkylene) polyol, diethyltoluenediamine and apolyoxypropylenediamine/metallic soap/polyether polyol blend.

The mixture may also include a polyether siloxane surfactant, blowingagents, catalysts, surface-active additives, flame retarding agents, UVstabilizers, plasticizers, dyes, fillers, mold release agents.

When reinforcing fillers are used, as is conventional, they may be usedin an amount from 4-30% weight based upon the weight of the molded part.Such a filler may be glass fibres, glass flakes, mica, wollastonite,talc, calcium carbonate, carbon fibres.

Fillers used to enable density reduction microspheres, may be used in anamount from 0.5%-6% weight based upon the weight of the molded part. Themicrospheres should be used in an amount enabling maximum weightreduction without detriment to its strength, impact resistance andpainted appearance. The microspheres should not crush or collapse undermoulding, trimming, sanding or related operations. Nor should themicrospheres cause roughness or pitting on the surface of the paintedproduct. In order to achieve these goals, the hollow microspheres shouldhave a maximum size of 120 microns. They may have a density of 0.2-1.0preferably of 0.38-0.60. The lower limit of compressive strength of themicrospheres may be about 4,000 psi, it may be preferred that they havea compressive strength of about 10,000 psi. Examples of suitablemicrospheres are S-60 and/or S-38 glass microspheres marketed by 3MIndustrial Specialties Division (S-60 and S-38 are Trade Marks). Thesecommercially available microspheres are hollow thick-walledsoda-lime-borosilicate glass microspheres. The particle sizedistribution of these types of microspheres is 50% greater than 30microns, with no more than 8% greater than 62 microns and a maximumparticle size of 88 microns. The particle size distribution of the abovementioned S-60 and S-38 microspheres is especially advantageous forpolyol slurry viscosity and maintaining a continuous outer skin capableof quality painting. The compressive strength of the S-seriesmicrospheres is 10,00 psi, which is a preferred property to preventingbreakage and thus pitting on the surface of the painted product.

The invention includes products made by the processes of the inventionespecially those products requiring to pass an on-vehicle 5 mph crashtest. In order to maintain the required impact properties of thecomponents and enable a lower density product to be made, the selectionof the reinforcing filler is critical. Rrimglos I 10013, a surfacemodified acicular fine particle size wollastonite was found to exhibitexcellent reinforcing characteristics, allow excellent paintability andgloss and provide the required impact resistance for the moldedpolyurethane fascias. Rrimglos, a product of Nyco Minerals Inc,(Rrimglos is a Trade Mark), has been shown to exhibit superiorproperties in polyurethane over a number of other common reinforcingfillers such as milled glass fibres, wollastonite etc.

The invention is further illustrated, but is not limited by thefollowing examples in which all parts and percentages are by weightunless otherwise specified.

EXAMPLES Example 1

An isocyanate-reactive component was prepared using 76,775 parts ofpolyether polyol, 16 parts of diethyltoluenediamine, 7 parts ofpolyoxypropylenediamine / metallic soap/ polyether polyol, 0125 parts ofcatalyst T-12 and 0.10 parts of catalyst Dabco 33LV (Dabco is a TradeMark). A polyol slurry was prepared as would normally be used in themolding of a urethane RRIM product. To the above polyol blend was addedRrimglos I 10013 (Nyco Minerals Inc.) and S-60 hollow glass microspheres(3M Scotchlite Glass Bubbles) (Scotchlite is a Trade Mark). The weightratio of polyol blend to Rrimglos to the microspheres was 100 to 9.8 to3.3, respectively.

The polyol slurry was charged into a RIM machine. Nitrogen was dissolvedinto the slurry via a sparger stone. Without the use of microspheres avoid free part can be made at a slurry density nucleated to 0.70 g/cc.With the use of microspheres a void free part was made at a slurrydensity nucleated to 0.55 g/cc.

The slurry was combined with a commercially available aromaticisocyanate prepolymer, Mondur PF, at a ratio of 44.7 parts isocyanate to100 parts of polyol slurry. Urethane parts were molded in the EN-114Ford Rear steel mold (Mondur is a Trade Mark). The mold temperature was68 deg C. The chemical temperatures were maintained at 37 to 43 deg. C.for the isocyanate and 41 to 62 deg. C for the polyol slurry. The mixingpressures were 1700 psi for each component. Urethane parts of excellentquality, physical and dimensional properties were produced. Up to a 10%density reduction was achieved over conventional RRIM reinforced with11,25% milled glass fibre.

After heavy sanding on the wheel-well parting lines, the parts were postcured for 40 minutes at 130 deg. C. The parts were then conventionallypower-washed and painted. The parts exhibited greater gloss anddistinction of image (DOI) than RRIM parts reinforced with 11.25% milledglass fibre. Areas along the wheel-well which had been exposes to heavysanding did not exhibit any "pitting" due to microsphere or skinbreakage.

Example 2

An isocyanate-reactive component was prepared using 76,525 parts ofpolyether polyol, 16.25 parts of diethyltoluenediamine, 7 parts ofpolyoxypropylenediamine / metallic soap/polyether polyol, 0.125 parts ofcatalyst T-12 and 0.10 parts of catalyst Dabco 33LV. A polyol slurry wasprepared as would normally be used in the molding of a urethane RRIMproduct. To the above polyol blend was added Rrimglos I 10013 (NycoMinerals Inc.) and S-38 hollow glass microspheres (3M Scotchlite GlassBubbles). The weight ratio of polyol blend to Rrimglos to themicrosphere was 100 to 9.8 to 2.1, respectively.

The polyol slurry was charged into a RIM machine. Nitrogen was dissolvedinto the slurry via a sparger stone. Without the use of microspheres avoid free part can be made a slurry density nucleated to 0.70 g/cc. Withthe use of microspheres a void free part was made at a slurry densitynucleated to 0.58 g/cc.

The slurry was combined with Mondur PF (a commercially availablearomatic isocyanate prepolymer) at a ratio of 45.7 parts isocyanate to100 parts of polyol slurry. Urethane parts were molded in the EN-114Ford Rear steel mold. The mold temperature was 68 deg. C. The chemicaltemperatures were maintained at 37 to 43 deg. C for the isocyanate and41 to 62 deg. C for the polyol slurry. The mixing pressures were 1750psi for each component. Urethane parts of excellent quality, physicaland dimensional properties were produced. Up to a 9% density reductionwas achieved over conventional RRIM reinforced with 11.25% milled glassfibre.

After heavy sanding on the wheel-well parting lines, the parts were postcured for 40 minutes at 130 deg. C. The parts were then conventionallypower-washed and painted. The parts exhibited greater gloss and DOI thanRRIM parts reinforced with 11.25% milled glass fibre. Areas along thewheel-well which had been exposed to heavy sanding did not exhibit any"pitting" due to microsphere or skin breakage. Example 3

An isocyanate-reactive component was prepared using 72.775 parts ofpolyether polyol, 20 parts of diethyltoluenediamine, 7 parts ofpolyoxypropylenediamine / metallic soap / polyether polyol, 0.125 partsof catalyst T-12 and 0.10 part of catalyst Dabco 33LV. A polyol slurrywas prepared as would normally be used in the molding of a urethane RIMproduct. To the above polyol blend was added S-60 hollow glassmicrospheres (3M Scotchlite Glass Bubbles). The weight ratio of polyolblend to the microsphere was 100 to 0.80, respectively.

The polyol slurry was charged into a RIM machine. Nitrogen was dissolvedinto the slurry via a sparger stone. Without the use of microspheres avoid free part can be made at a slurry density nucleated to 0.65 g/cc.With the use of microspheres a void free part was made at a slurrydensity nucleated to 0.62 g/cc.

The slurry was combined with Mondur PF (a commercially availablearomatic isocyanate prepolymer) at a ratio of 58.5 parts isocyanate to100 parts of polyol slurry. Urethane parts were molded in the SN-95Mustang GT steel mold. The mold temperature was 68 deg. C. The chemicaltemperatures were maintained at 37 to 43 deg. C for the isocyanate and41 to 62 deg. C for the polyol slurry. The mixing pressures were 1500psi for each component. Urethane parts of excellent quality, physicaland dimensional properties were produced. A 5% weight reduction wasachieved over unfilled RIM.

We claim:
 1. A method of preparing a low density rigid article of foamedpolyurethane having an outer continuous surface skin, the mixturecomprising:selecting and forming a mixture of polyisocyanate and anisocyanate-reactive component to form a low density rigid foamed moldinghaving a continuous skin; subjecting the mixture to a reactive injectionmolding process to form a foamed rigid product having a continuous skin;said mixture including from 0.5% to 6% by weight, based upon the weightof the mixture of hollow glass microspheres having a maximum size of 120microns and a compressive strength of at least 4000 psi.
 2. A method asclaimed in claim 1 in which the isocyanate-reactive component comprises(i) at least one compound containing at least two isocyanate-reactivegroups, and (ii) dissolved nitrogen in an amount sufficient to produce amolded product having a density of at least 0.8 g/cc.
 3. A method ofpreparing a low density rigid article as claimed in claim 1 in which thepolyisocyanate is 4, 4'-diphenylmethane diisocyanate (MDI) prepolymer.4. A method of preparing a low density rigid article as claimed in claim1 in which the isocyanate-reactive component is a polyether polyolsystem containing minimally an aliphatic amine and an aromatic diamine.5. A method of preparing a low density rigid article as claimed in claim1 in which the mixture also includes from 4-30% of an inorganicreinforcing filler.
 6. A method of preparing a low density rigid articleas claimed in claim 5 in which the inorganic reinforcing filler isselected from glass fibres, glass flakes, mica, wollastokup,wollastonite, talc, calcium carbonate, carbon fibres.
 7. A method ofpreparing a low density rigid article as claimed in claim 1 in whichsaid hollow glass microspheres have a size from 40 to 90 microns.
 8. Amethod of preparing a low density rigid article as claimed in claim 1 inwhich the hollow glass microspheres have a density of 0.2 to 1.0 g/cc.9. A method of preparing a low density rigid article as claimed in claim8 in which the hollow glass microspheres have a density of 0.38 to 0.6g/cc.
 10. A method of preparing a low density rigid article as claimedin claim 1 in which the hollow glass microspheres are present in aproportion of about 2% by weight of the molded product.
 11. A method ofpreparing a low density rigid article as claimed in claim 1 in which thehollow glass microsphere has a compressive strength of about 10,000 psi.